The use of ferroelectric capacitors in a one device cell for dynamic random access memory (DRAM) or non-volatile random access memory (NVRAM) applications is well known. These known ferroelectric cells have limited use of two storage mechanisms to store one bit of information per one device cell.
In the article "A Ferroelectric DRAM Cell for High Density NVRAMS", by R. Moazzami et al, VLSI Symposium, May 1990, pp. 15 and 16, there is described a ferroelectric nonvolatile RAM (FNVRAM) which normally operates as a conventional DRAM yet also exploits the hysteresis loop of ferroelectric materials for nonvolatile operation upon command or power failure with the state of the cell being read and written back as one of two permanent polarization states of the ferroelectric film.
In U.S. Pat. No. 4,055,837 by K-U. Stein et al, which issued on Oct. 25, 1977, there is disclosed a single transistor memory including an MNOS capacitor wherein the dielectric has a plurality of selective states and a write line.
In U.S. Pat. No. 5,163,021 by S. Mehrotra et al, which issued on Nov. 10, 1992, there is disclosed an EEPROM cell having a floating gate which stores a plurality of bits by establishing different threshold levels.
U.S. Pat. No. 5,136,534 by J. M. McDavid et al, issued on Aug. 4, 1992, discloses a memory cell having a storage layer which may be a dielectric or a ferroelectric material and thereby used as either a dynamic random access memory cell or a nonvolatile memory cell.
U.S. Pat. No. 5,038.323 by L. J. Schwee, which issued on Aug. 6, 1991, discloses a non-volatile memory cell having a ferroelectric capacitor wherein one electrode of tile capacitor has a fixed voltage of approximately one-half the supply voltage supplied to the memory cell.
U.S. Pat. No. 5,121,353 by K. Natori, which issued on Jun. 9, 1992, discloses a ferroelectric capacitor memory circuit which includes a setting MOS field effect transistor for setting both electrodes of the ferroelectric capacitor at the same potential when the cell is not accessed.